Pink Noise

Pink noise is related to White Noise, but it is "colored" somewhat. White noise is noise which is uniform across the audible frequency for humans (nominally 20 Hz to 20,000 Hz), though white noise source for canines or other animals can be develeoped. "pure" TV static through a full-range audio system often closely approximates white noise. Pink noise is somewhat non-uniform, in accordance with the response curve of the human ear, that is the tendency of most ears to detect sounds at some frequencies (especially the frequencies involved in voice communications) better than at others. Pink noise emphasizes those frequencies to, for example, improve the effectiveness of sound masking systems used to promote acoustic privacy in open office areas.

http://www.embedded.com/2000/0003/0003spectra.htm offers this definition ...

Pink noise has equal energy per octave instead of equal energy per frequency like white noise. In other words, its energy is equal to 1/f, which describes a -3dB/octave response. This means that the frequency at each octave of increasing frequency should contain half the power of the preceding one. Since there are double the number of frequencies within the octave, the power level of the octave as a whole remains the same.

Pink noise is quite useful for equalizing audio systems. If you inject pink noise and measure the sound level using an octave (or, better, third-octave) SPL meter, you can adjust the sliders of your octave (or third-octave) graphic equalizer until the SPL meter shows a horizontal line.